It is interesting that if excessive noise reduction is applied to hair, when the image is downsampled, the hair looks greasy, as if it needs a shampoo and blow-dry.

(a) Shot at high resolution, all cameras with sensor this size clump at high resolution. It will be a lot better at M4:3 ...

(b) The hair looks fine to me when downsized.

If you look at the fill sized images ... I think it's pretty obvious that she has not washed her hair for this shoot. The clumping is not just caused by NR ... there are many real clumps in there and that darkening is a classic sign of dirty hair ...